Two other heating pieces already exist here. Turning the heating on is the first fire, the programmer and the October cap. A boiler that will not fire is ignition and lockout. This page is the alarm on the wall: whether it still works, what the sound means, and when you leave the house instead of bleeding a radiator. It is not a quote, not a grant decision, and not a dispatch line.
On 14 September 2026, at the start of Gas Safety Week (14 to 20 September), the Health and Safety Executive published new conviction figures for illegal gas work: 17 people sentenced since the start of 2025, against three in 2022/23 and four in 2023/24. HSE’s Principal Inspector of Gas Safety, Steve Critchlow, put it in the same week as falling temperatures and rising bills. That is the reason to test the alarm tonight, not to run the heating harder. If you already know you need a number for planned work, open plumbing and heating and use the number on the card.
Why the first overnight fire is different
A short test in the afternoon tells you the burner will light. Overnight heating is the first time a flue, a sealed room and a sleeping household share several hours. Carbon monoxide is colourless and has no smell. HSE still calls it the silent killer. Its domestic gas pages say around seven people a year die from gas-related carbon monoxide poisoning, and that appliances and flues should be safety-checked at least once every 12 months. An alarm is the thing that can wake you. It is not the service.
UKHSA’s reading of the Office for National Statistics figures for deaths registered in 2024 puts accidental carbon monoxide poisoning in England and Wales at around 25 deaths a year from all sources, not only boilers. Those are different counts. Neither is a reason to invent a local death toll for your street. Both are a reason not to treat a silent plastic box on a shelf as decoration.
The week that just closed used the line “Take No Chances”. CIPHE repeated it on 14 September 2026: book the annual check, and check the engineer is registered for the work. That is the campaign. This page is the five-minute check you can do before the first night you leave the heating on.
How to test the alarm tonight
Do this before you set a long heating period. You are checking the unit, not the boiler. Stay on the floor. Do not take a case off a gas appliance.
- Find every carbon monoxide alarm, not only the one in the kitchen. A combi in a cupboard, a gas fire in the living room and a boiler in the loft each need the room they sit in to be covered. England’s landlord rule is a room used as living accommodation with a fixed combustion appliance, excluding a gas cooker. Owner-occupiers should still treat every fired appliance as a room that needs a working alarm.
- Press the test button and hold it for the time the label says. You should get a loud alarm and, on most units, a flashing light. No sound means a dead battery, a failed unit, or a button that never reached the board. Replace it before you run the heating overnight.
- Read the expiry or replace-by date on the back or side. Gas Safe Register’s consumer advice puts a typical life at five to ten years. The date on your unit is the authority, not a rule of thumb. An end-of-life chirp is a replacement, not a reset.
- Look for British Standard EN 50291 and an approval mark such as a Kitemark. HSE’s domestic gas FAQ says to buy to that standard, that alarms cost from about £15 in ordinary hardware shops, and that an alarm is not a replacement for a Gas Safe safety check.
- Check the position against the maker’s card. The government’s landlord booklet for the 2022 amendment, in force from 1 October 2022, says that in general a carbon monoxide alarm sits at head height, on a wall or a shelf, about 1 to 3 metres from the appliance. A unit stuffed behind the sofa or still in its box does not count.
A smoke alarm is a different sensor. It will not warn you about carbon monoxide. A colour-change spot card will not wake anyone. Test the audible unit you actually have.
What the sound actually means
People treat every beep as “the alarm going off”. That is how a low battery gets ignored until 2am, and how a real alarm gets dismissed as the same chirp. Listen once, in daylight, so you know the difference.
| What you hear | Likely meaning | Next step |
|---|---|---|
| A short chirp every minute or so, often at night | Low battery or end of life | Change the battery or replace the unit. Do not tape it |
| A loud, continuous or repeating full alarm | The sensor thinks carbon monoxide is present | Leave. Call 0800 111 999. This page is over |
| Nothing when you hold the test button | Dead power, a failed sensor, or a unit past its date | Replace it before overnight heating |
| Alarm only when you press test, then silence | The sounder works | Still check the date and the room it covers |
| You smell gas, alarm silent | A leak of unburnt gas. That is not carbon monoxide | Same emergency number. Leave. Do not hunt with a lighter |
GOV.UK’s carbon monoxide briefing is explicit: unignited gas does not contain carbon monoxide. A smell of gas and a sounding CO alarm are different problems that share one number. Do not wait to decide which label fits before you leave.
If the alarm sounds, leave first
The National Gas Emergency Service is 0800 111 999, free, 24 hours. NHS carbon monoxide advice, last reviewed on 16 December 2025, tells you to call that line if you think a gas appliance is leaking carbon monoxide. National Gas says the same number covers a gas emergency, a suspected carbon monoxide emergency, and a struck pipeline.
- Stop using the appliances. Switch them off if you can do so without delaying the exit. Open doors and windows if that is on the way out.
- Get everyone into fresh air, including pets. Stay calm. Do not run. National Gas tells you not to raise your heart rate on the way out.
- Do not use electrical switches, naked flames or a mobile that makes you linger by the meter. Turn the gas off at the meter only if you already know where it is and it does not take you into a cellar you would otherwise skip.
- Call 0800 111 999 from outside. HSE also publishes a Gas Safety Advice Line on 0800 300 363 for non-emergency questions in office hours. An alarm that is sounding is the emergency number.
- Do not go back in until the people on that call, or the engineer they send, say so. Fresh air does not treat exposure by itself. Seek medical help.
Call 999 or go to A&E if anyone is finding it hard to breathe, has become confused, has lost consciousness, feels weak, or has chest or muscle pain. NHS says not to drive yourself. A directory card is not an ambulance.
Symptoms that are not “just a cold”
NHS lists headache, dizziness, feeling sick, weakness, tiredness and confusion, chest and muscle pain, shortness of breath, flushing, and loss of vision. The clue is the pattern: several people, or a pet, feel worse in the house and better outside. HSE’s carbon monoxide pages say the early signs are easy to confuse with flu, food poisoning or tiredness. That is why the alarm exists. Do not diagnose from a webpage while you stay in the room.
If you think you have symptoms but nobody is in immediate danger, NHS 111 is the non-999 route. Tell them you suspect carbon monoxide. Then treat the house as the source until a registered person has said otherwise. Do not “air it for an hour and see” overnight with the heating still on.
Sooty staining around an appliance, a lazy yellow flame on a burner that should burn blue, or condensation that stays on the windows in a room that used to clear, are reasons to stop using that appliance and call. They are not a DIY clean of the flue. Opening the case is gas work.
The register, the landlord, and a flyer on the lamp-post
Anyone doing gas work as a business must be on the Gas Safe Register. That is the Gas Safety (Installation and Use) Regulations 1998, not a badge this site sells. HSE’s 14 September 2026 release is about people who were not on that register: a flyer with a faked mark, a man who had dropped off the register and kept working, a boiler left immediately dangerous. Check the engineer on gassaferegister.co.uk or by calling 0800 408 5500, and look at the work types on the back of the ID card. “Plumber” on a van is not the same as a current registration for boilers.
Landlords in Great Britain must arrange an annual gas safety check on appliances and flues they provide, keep the record for two years, and give existing tenants a copy within 28 days of the check. Owner-occupiers do not get a certificate by law, but HSE still tells you to have the same annual look. A working alarm does not complete that visit. The Gas Safe notes are the legal register page. Stay there if your question is who may break a gas joint. Stay here if your question is whether the box on the wall will shout.
From 1 October 2022, relevant landlords in England must also provide a carbon monoxide alarm in any living-accommodation room that contains a fixed combustion appliance, other than a gas cooker, and must repair or replace a faulty alarm once they are told. Scotland, Wales and Northern Ireland publish their own alarm rules. If you rent, report a failed test to the landlord. Do not treat a supermarket alarm as a substitute for the duty they already have, and do not book a Gas Safe visit they have not agreed unless the emergency line has already told you to get out.
When to put the test button down and call
Stop the homeowner sequence if any of these apply. They are not “try a new battery in the morning” problems.
- The carbon monoxide alarm sounds on its own, not only under your finger. Leave. 0800 111 999.
- You smell gas, hear a hiss you cannot place, or someone in the house has the symptoms above that ease outdoors.
- The alarm has no power, is past its date, or you have no alarm in a room with a boiler, fire or other fixed combustion appliance, and you intended to run the heating overnight anyway. Fit a compliant unit or stay with another plan until you have one.
- A visitor offers to “just look at the flue” without a Gas Safe card, or a social-media flyer is the only credential. HSE’s week was about that person. Do not let them through the door.
- You are a tenant and the alarm failed, is missing, or you have not seen this year’s gas safety record. Tell the landlord what you tested and what you heard. The annual check is their duty, not a job you should quietly commission.
If the house is simply cold and the alarm tested fine, that is the first-fire guide or the lockout guide, not this page. The heating power calculator can help you describe the size of the house on a later call. It does not tell you whether carbon monoxide is in the room.
What to have on the call
For 0800 111 999, have the address, whether anyone feels unwell, whether you can smell gas, and whether the carbon monoxide alarm is still sounding. That call is the emergency service, not this directory.
For a planned check after the alarm tested fine, have the boiler or fire make and model, the room it sits in, the alarm’s expiry date, whether you are a tenant, and whether last year’s gas safety record is in the house. Ask whether the person coming is Gas Safe for that appliance type, and whether the first figure is plus VAT. Ask to see the card at the door.
This site does not email the business. Open the directory — for example plumbing in London or plumbing in Manchester — and use the number on the card. A Gas Safe field on a profile only means the field is present. Check the register yourself.
Questions before you run the heating overnight
These answers stay inside what HSE, NHS, GOV.UK and Gas Safe Register have already published. They are not a survey.
Does a working carbon monoxide alarm replace a boiler service? No. HSE says an alarm is a warning, not a substitute for a safety check by a Gas Safe registered engineer at least once every 12 months. Press the test button tonight. Book the service separately. This site does not sell that visit.
What should I do if the carbon monoxide alarm sounds? Stop using appliances, get everyone into fresh air, and call 0800 111 999. Do not use electrical switches on the way out. Call 999 if anyone is struggling to breathe, confused, weak, or has chest pain. A list on this site is not an emergency line.
Must a landlord fit a carbon monoxide alarm? In England, from 1 October 2022, relevant landlords must put one in any room used as living accommodation that contains a fixed combustion appliance, except a gas cooker. Other UK nations have their own rules. Tell the landlord if a test fails.
How do I check the engineer is on the Gas Safe Register? Ask for the ID card and the work types on the back. Check the number on the Gas Safe Register site or 0800 408 5500. HSE’s 14 September 2026 note is about people who faked that mark.
Will this site send someone if the alarm sounds? No. Leave and use the emergency number. For planned work, you open a list and place the call yourself.
Need a number after the alarm test?
Open plumbing and heating, pick the city, and ask to see a Gas Safe card. You place the call. If the alarm is sounding, use 0800 111 999 instead.